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Why does everyone get performance wrong?

About the Talk

Cache hit ratios, requests per second, load average… these are all half measures when it comes to performance analysis. What is more important is:

How long a task takes to complete (response time).
How many tasks are you completing per unit of time (throughput).
What is the maximum number of tasks you can complete (capacity).

Understanding what you are measuring is key for successful optimization. For example – many developers make the mistake of optimizing for ‘throughput’, or looking at system ‘capacity’ numbers (loadavg, util %). What they don’t realize is as throughput increases – response time goes up (think of this as the same traffic-jam effect from many cars going down a highway). It’s also easy to fall into the trap of optimizing for the average user, when it’s more important to optimize for all users.